Microstructure and mechanical properties of a novel selective laser melted Al-Mg alloy with low Sc content

The novel Al-4.5Mg-0.32Sc-0.66Zr alloy was successfully fabricated by selective laser melting. The minimum porosity of 0.5% was obtained for a laser power of 180 W, a scan speed of 220 mm s−1 and a hatch distance in the range of 0.13-0.15 mm. The microstructure of the as-fabricated alloy consists of aluminum solid solution grains with a typical bimodal size distribution at about 3-5 m and 1 m. Nanosized Al3(Sc, Zr) particles with a size of about 20-50 nm mainly formed on grain boundaries after one stage annealing at 360 °C/6 h. Homogenously distributed Al3(Sc, Zr) dispersoids 5-8 nm in diameter formed after two stage annealing 300 °C/3 h + 360 °C/4 h. As result the plasticity is 6% higher after two-stage annealing than after one-stage annealing. The yield strength and the ultimate tensile strength after both heat treatments are 424-438 MPa and 465-480 MPa, respectively. The optimum strength and plasticity combination was obtained after two-stage annealing in the samples fabricated in the XY direction: YS = 435 MPa, UTS = 478 MPa and El. = 16%.